I know the title sounds very cliché and hyperbolic but please stick with me, I honestly think this is at least top 5 dumbest reasons someone has lost a shiny ever
I was big on watching Shiny hunting reactions and one thing i basically always saw was the shiny hunters would use 2 moves, false swipes to get them down to 1hp, and substitute to extend the time spent in the battle with minimal damager taken.
So when I first got Pokémon shield and encountered a random shiny Hoothoot around the age of 11-12 you can image how hyped I was when I hit that random shiny encounter of 1/4096. After a good time of running around my living room I sat down and realized I didn't have either of the two moves I had seen the streamers use.
While looking though my bag to see what Pokeballs I had I saw it. "PokeDoll". My mind went "Oh! Pokedoll! That's what the streamers use! Its a doll that is a pokemon" so without reading what the item does like a dumb kid, I pressed use. I sat there and watched the screen say the 4 words that still haunt me
"You got away safely!"
I say this is one of the dumbest ways ever because it was the fact I understood everything about shiny's, I knew how rare they were so I didn't run away thinking it was a "visual glitch", I knew the strategies on how to catch them and it wasn't like I was looking away from the screen so I 100 percent knew I encountered one and didn't just run away from it not realizing I encountered one.
Happy Ending though!
Running away from that Hoothoot gave me motivation to 100 percent complete the dex, kill 1000+ Noctowls and finally get my shiny Noctowl so now my dex shows both the shiny Hoothoot and Noctowl, finally getting my get back!
by New_Climate_3758